EP3738192A1

EP3738192A1 - In-wheel electric motor maintenance integration

Info

Publication number: EP3738192A1
Application number: EP18706584.2A
Authority: EP
Inventors: Raphael CONNES; Gasper SUSTERSIC; Gorazd GOTOVAC; Senad OMEROVIC; Ales Vlaj
Original assignee: Elaphe Propulsion Technologies Ltd
Current assignee: Elaphe Propulsion Technologies Ltd
Priority date: 2018-01-09
Filing date: 2018-01-09
Publication date: 2020-11-18
Anticipated expiration: 2038-01-09
Also published as: EP3738192B1; WO2019139545A1

Abstract

The present invention relates to a rotor-stator combination for an in-wheel electric motor assembly of a vehicle, the in-wheel electric motor assembly comprising a bearing system (10) mounted to a knuckle of the vehicle for rotatably coupling a wheel rim to the knuckle of the vehicle, a brake, and the rotor-stator combination comprising a rotor and a stator, wherein rotor and stator are arranged concentrically with respect to each other such that rotor and stator share a common motor axis, and wherein the rotor-stator combination has a first axial end facing the vehicle knuckle in a fully assembled state of the in-wheel electric motor assembly and a second axial end facing away from the vehicle knuckle in a fully assembled state of the in- wheel electric motor assembly, wherein the stator comprises stator mounting points for mounting the rotor-stator combination to the vehicle knuckle, wherein the rotor-stator combination has a hollow interior adapted to receive the bearing system and the brake in a fully assembled state of the in-wheel electric motor assembly, and wherein the rotor comprises a plurality of rotor fixation holes and the stator comprises a plurality of stator fixation holes, wherein the rotor is lockable to the stator such that the concentric arrangement of rotor and stator is maintained without a bearing being arranged between rotor and stator, wherein locking the rotor to the stator is achievable by inserting a plurality of locking tools into the plurality of rotor fixation holes and into the plurality of stator fixation holes, wherein each of the plurality of locking elements is inserted into one of the plurality of rotor fixation holes and into a corresponding one of the plurality of stator fixation holes. According to the present invention, an opening of the rotor-stator combination at the first axial end of the rotor-stator combination facing the knuckle and leading into the hollow interior of the rotor-stator combination is designed such that the rotor-stator combination can be mounted to and dismounted from the vehicle knuckle as a unit without the need to remove the bearing system and/or the brake from the vehicle knuckle, wherein the stator mounting points are arranged at such a distance from the motor axis that the stator mounting points do not interfere with the bearing system and brake when the rotor-stator combination is mounted to or dismounted from the vehicle knuckle.

Description

In-wheel electric motor maintenance integration

The present invention relates to the field of electrical machines, focusing on mechanical design of an in-wheel motor that enables fast and convenient brake and bearing servicing, in-wheel motor tuning, servicing, replacement, assembly and testing in production. In particular, the present invention relates to a rotor-stator combination according to the preamble of independent claim 1 , to a system for assembling and/or servicing an in-wheel electric motor with such a rotor-stator combination according to claim 9, an in-wheel electric motor assembly of a vehicle with such a rotor-stator combination according to claim 14, a method for manufacturing a rotor- stator combination according to claim 17, and to a method of performing maintenance work on serviceable parts of an in-wheel electric motor assembly of a vehicle according to claim 23.

Currently a couple of prevailing layouts are used for in-wheel motors where the majority of them could be divided into two groups. The first group being in-wheel motors that contain serviceable components which can be removed with intact rotor and stator bearing system, and the second group where the bearing system is affected by said removal. The invention of this patent falls within the latter group, where typical examples for serviceable components are the brake system and the bearing system. The description focuses mainly on braking system maintenance, while not being limited to it, it equally refers to the other serviceable components as well.

The access to the brake system with the purpose of tuning and quick servicing is very limited, especially when the whole brake system needs to be removed, serviced and mounted back, which is usually a complicated process and requires expensive tools. While performing any servicing on the brake system it is crucial to maintain a proper and uniform air gap between stator and rotor to achieve the appropriate accuracy of the assembly process. In the existing solutions with the integrated brake the in-wheel motor cannot be removed from the vehicle without also removing the brake system from the vehicle, which is also true when motor seals or bearings need to be serviced. The brake system has to be delivered and sold together with the in-wheel motor, otherwise complicated mounting procedures have to be performed by the customer, usually also including usage of complicated and expensive tools. Furthermore the braking system needs to be present in assembly when implementing procedures of production testing of the in-wheel motor.

US patent application US 20150137669 A1 which discloses a rotor-stator combination according to the preamble of independent claim 1 partially addresses the above described shortcomings as well as the need to include the brake system in maintenance and sales procedures while also reducing the complexity of the tools needed by allowing to remove one of the rotor structural parts using relatively simple“rotor/stator locking” flanges on the motor plane facing the inside of the vehicle. This is appropriate for a drum brake system, since there is sufficient access to the braking pads and other components by simply removing the drum, but for any substantial servicing of the disc brake (pad replacement, disc replacement, caliper servicing etc.) apart from removing the air from the hydraulic fluid circuit, the whole brake needs to be removed from the vehicle, in most cases also disconnected from the vehicle due to the inflexibility of hydraulics attachments. The solution described in US 20150137669 A1 is therefore not optimal for a motor with a disc brake. Furthermore, the proposed solution does not address the difficulty of removing the brake, since sensitive components such as seals and threadlocked screws need to be removed and reinstalled whenever such a removal and reinstallation of the brake is done. The use of the proposed“stator/rotor locking” flanges can sometimes be obstructed by the vehicle components and is therefore subject to vehicle- dependent customization which can be economically less favorable. International patent application WO 2009086884 A1 describes a solution for a quick service of the brake system made possible by removing the wheel rim from the wheel hub to gain the needed working space for servicing while the electric motor remains fastened to the vehicle knuckle. The assembly is overdetermined due to bearings being arranged both between axle and wheel hub and between rotor and stator of the electric motor such that the rotor cannot be fastened to the wheel hub or the wheel rim. The rotation of the rotor is transmitted to the wheel rim via form-locking elements on rotor and rim. The solution described in WO 2009086884 A1 requires radial and axial play between the form-locking elements of rotor and wheel rim. Furthermore, the proposed solution does not solve maintenance integration of the bearing system and the seals. The solution described in international patent application WO 1995000352 A1 includes a hollow bearing system, but it does not solve the problem of the brake integration and poorly solves the sealing problem, as it does not provide suitable solutions for the small diameter seals. KR100875004 focuses on in-wheel motor design for solving mounting problems in direction of minimizing the cumulative tolerance with various adaptations of assembly part joints relating to those of the prior art and thus not solving maintenance integration at all.

A rotor-stator combination according to the present invention is defined by independent claim 1.

The in-wheel electric motor design covered by this invention allows an easy to use locking tool for rotor and stator, with which it successfully solves the key problems of the mechanical design, as it allows shipping of the electric motor without mounted bearing system or the brake system, it also allows performance of the brake system maintenance tasks without disassembling a complete in-wheel electric motor or dismantling it from the vehicle. It protects all the parts from the mechanical damage, which could occur as the consequence of inappropriate fitting of the rotor onto the stator, and allows easy assembly of the in-wheel motor. In particular, the solution according to the present invention offers the advantage that the rotor-stator combination can be mounted to and dismounted from the vehicle knuckle as a unit. Contrary to the solution described in US 20150137669 A1 , it is not necessary to partly disassemble stator and/or rotor to get access to the serviceable parts received in the interior of the rotor-stator combination.

The stator can be mounted either directly to the vehicle knuckle or via a stator plate which is fixed to the vehicle knuckle. Preferably, both the rotor fixation holes and the stator fixation holes are evenly spaced over the circumference of the rotor-stator combination. The locking tool is preferably a stiff structure. According to another preferred embodiment of the invention, the rotor is an external rotor and comprises an external rotor portion enclosing the stator and a flange extending from the external rotor portion in a radial direction towards the motor axis, wherein the rotor fixation holes are through holes formed in the flange.

Further preferred embodiments of the rotor-stator combination are subject to the dependent claims.

According to a preferred embodiment of the invention, each of the rotor fixation holes is arranged at the same radial distance from the motor axis as the corresponding stator fixation hole such that the axes of said rotor fixation hole and said corresponding stator fixation hole coincide. Preferably, all rotor fixation holes and all stator fixation holes are arranged at the same radial distance from the motor axis. Further preferably, the axes of the rotor and stator fixation holes are parallel to the motor axis.

According to another preferred embodiment of the invention, an opening of each of the rotor fixation holes is surrounded by a first flat surface of the rotor that is perpendicular to the axis of the respective rotor fixation hole, wherein an opening of each of the stator fixation holes is surrounded by a second flat surface of the stator that is perpendicular to the axis of the respective stator fixation hole.

According to another preferred embodiment of the invention, the rotor fixation holes are located on an axial side surface of the rotor facing the rim, wherein the stator holes are located close to the axial side surface of the rotor facing the rim without obstructing the bearing system and the brake.

According to another embodiment of the invention, each of the rotor fixation holes comprises a threaded portion into which the corresponding locking tool can be screwed, wherein each of the stator fixation holes also comprises a threaded portion into which the corresponding locking tool can be screwed. According to an alternative embodiment of the invention, only the stator fixation holes comprise a threaded portion into which the corresponding locking tool can be screwed. Preferably, each of the rotor fixation holes comprises an axial portion of reduced inner diameter.

According to another embodiment of the invention, the rotor-stator combination further comprises a plurality of sealing plugs insertable into the plurality of rotor fixation holes in order to prevent dirt from entering through the rotor fixation holes into the interior of the electric motor during normal machine operation.

The present invention also provides a system for assembling and/or servicing an in-wheel electric motor, with a rotor-stator combination according to the invention and with a plurality of locking tools, wherein the rotor is locked to the stator for assembling and/or servicing purposes in that each of the plurality of locking elements is inserted into one of the plurality of rotor fixation holes and into a corresponding one of the plurality of stator fixation holes.

According to an embodiment of the system for assembling and/or servicing an in-wheel electric motor, each locking tool comprises a screw with a thread of size and type matching the size and type of the above mentioned threaded portion of the stator fixation holes, and an externally threaded tube, wherein the size and type of an external thread of the tube matches the size and type of the above mentioned threaded portion of the rotor fixation holes, wherein the tube, on one end thereof, comprises an axial portion of reduced inner diameter for limiting axial movement of the screw, and wherein the tube, on another end thereof, comprises a specific shape for mounting the tube onto the rotor fixation hole.

According to an alternative embodiment of the system for assembling and/or servicing an in- wheel electric motor, each locking tool comprises a screw with a thread of size and type matching the size and type of the above mentioned threaded portion of the stator fixation holes, wherein a head of the screw is smaller in diameter than a diameter of an axial portion of the rotor fixation holes with non-reduced inner diameter.

According to another alternative embodiment of the system for assembling and/or servicing an in-wheel electric motor, the diameter size of the rotor holes follows standardized interference fit recommendations so as to enable tight fit with the locking tool without the need for sealing plugs during the electrical machine operation, wherein the diameter size of the stator holes follows standardized interference fit recommendations so as to enable loose fit with the locking tool. In this embodiment, no threaded portions of the rotor and stator fixation holes are necessary. Preferably, the locking tool comprises a tube and an inner shaft, wherein the tube has an outer diameter of a size following standardized interference fit recommendations enabling tight fit with the rotor fixation holes, wherein said tube comprises an inner diameter of a size following standardized interference fit recommendations enabling loose fit with the inner shaft, and wherein said inner shaft has a diameter of a size following standardized interference fit recommendations enabling loose fit with the stator holes.

The present invention also provides an in-wheel electric motor assembly of a vehicle, comprising a bearing system mounted to a knuckle of the vehicle for rotatably coupling a wheel rim to the knuckle of the vehicle, a brake, and a rotor-stator combination according to the invention as described above.

According to a preferred embodiment of the in-wheel electric motor assembly, the brake comprises a brake disk and a caliper, wherein the in-wheel electric motor assembly further comprises a seal or multiple seals or other serviceable components, and wherein the bearing system, the brake, the seal of multiple seals and the other serviceable components are not removable while the stator is attached via the stator mounting points to the vehicle. Preferably, the bearing system is interchangeable with another bearing system design using a custom adapter, a change of the stator plate, or a different design of respective vehicle attachment points, wherein the brake disc and the caliper are interchangeable with another brake disc and caliper design using a custom adapter, a change of the stator plate, or a different design of respective vehicle attachment points.

The present invention also provides a method of manufacturing a rotor-stator combination, particularly according to one of the embodiments described above, the method comprising the steps of mounting a rotor and a stator on a centering arrangement, locking relative position of rotor and stator with at least one locking tool, and detaching the locked rotor-stator combination from the centering arrangement.

According to a preferred embodiment, the centering arrangement provides radial and axial constraints for the relative position of rotor and stator and allows relative rotation of rotor and stator.

According to another preferred embodiment, the locking step comprises mounting a plurality locking tools to a plurality of rotor fixation holes and a plurality of stator fixation holes that are evenly spaced around the circumference of the rotor-stator combination.

According to another preferred embodiment, an intermediate step of rotor and stator assembly dynamic testing is performed before the locking step. According to another preferred embodiment, the centering arrangement is reused for the manufacturing of another rotor-stator combination after the locked rotor-stator combination has been detached from the centering arrangement.

According to another preferred embodiment, the method further comprises shipping the locked rotor-stator combination without installing a bearing system or a brake system to the rotor-stator combination.

The present invention also provides a method of performing maintenance work on serviceable parts of an in-wheel electric motor assembly of a vehicle, particularly according to one of the embodiments described above, the method comprising the steps of removing a vehicle wheel of the in-wheel electric motor assembly, locking relative position of a rotor and a stator of a rotor- stator combination of the in-wheel electric motor assembly with at least one locking tool; and unmounting the rotor-stator combination from mounting points of the vehicle and moving the rotor-stator combination aside without disconnecting it from the vehicle, thereby enabling maintenance of the serviceable components such as, for example, a bearing system or a brake.

According to a preferred embodiment, removing the vehicle wheel comprises unscrewing rim bolts and removing a rim of the vehicle wheel, wherein the locking step comprises mounting a plurality locking tools to a plurality of rotor fixation holes and a plurality of stator fixation holes that are evenly spaced around the circumference of the rotor-stator combination.

According to another preferred embodiment, sealing plugs are removed from the rotor fixation holes before mounting the plurality of locking tools to the plurality of rotor fixation holes and the plurality of stator fixation holes.

According to another preferred embodiment, the unmounting step comprises removing stator plate bolts and stud bolts.

Exemplary embodiments of the present invention are illustrated by way of example in the accompanying drawings in which:

Figure 1 is a partial axonometric exploded representation of an in-wheel electric motor assembly according to the invention seen from the rim side;

Figure 2 is a partial axonometric exploded representation of the in-wheel electric motor assembly shown in Fig. 1 seen from the vehicle side; Figure 3 is a sectional representation of the rotor-stator combination of the in-wheel electric motor assembly from Figs. 1 and 2 with a first embodiment of a locking tool for locking the rotor to the stator;

Figure 4 is a sectional representation of the rotor-stator combination of the in-wheel electric motor assembly from Figs. 1 and 2 with a second embodiment of the locking tool;

Figure 5 is a sectional representation of the rotor-stator combination of the in-wheel electric motor assembly from Figs. 1 and 2 with a third embodiment of the locking tool;

Figure 6 is a sectional exploded representation of the first embodiment of the locking tool;

Figure 7 is a sectional exploded representation of the third embodiment of the locking tool;

Figure 8 is a visualization of one of the steps of a method of manufacturing the rotor-stator combination;

Figure 9 is a visualization of another step of the method of manufacturing the rotor-stator combination;

Figure 10 is a visualization of another step of the method of manufacturing the rotor-stator combination;

Figure 1 1 is a visualization of another step of the method of manufacturing the rotor-stator combination.

Identical or corresponding elements have the same reference signs throughout the description unless indicated otherwise.

The presented innovation relates to the usage of an easy to use locking tool (3 - Figure 1 ) for locking electrical machine position of stator (2 - Figure 1 ) and rotor (1 - Figure 1 ), by means of matching fixing points mounted from the external side of the vehicle, where there are usually no obstructive elements.

The rotor (1 ) comprises special features or in other words fixing points for attachment of a multiple locking tools (3), where these special features comprise flat surfaces (1 1 - Figure 1 ). Each of these flat surfaces comprises a perpendicular rotor fixation hole (12 - Figure 1 ). These special features are located on the axial side of the rotor facing a rim (7 - Figure 1 ) and can be covered by sealing plugs (8 - Figure 3) during the electrical machine operation, depending on the chosen locking tool variant. If the locking tool variant includes sealing plugs then those have to be removed before maintenance process can start. The stator (2) in similar way comprises special features, or in other words fixing points for attachment of multiple locking tools (3). These special features are located on a flat surface (21- Figure 1 ) parallel to the flat surfaces of the rotor (1 1 ) when rotated by an appropriate angle, where said flat surface comprises perpendicular stator fixation holes (22 - Figure 1 ). These stator fixation holes on the flat surface are located close to the axial side surface (16 - Figure 1 ) of the rotor (1 ) facing the rim (7) not being obstructed by any elements. In this way the stator fixation holes are arranged at the same radial distance from the motor axis as the rotor fixation holes and can be aligned in the circumferential direction with the rotor fixation holes by means of rotation of the rotor on its axis (13 - Figure 1 ).

The stator (2) also contains mounting points (23 - Figure 2) for attachment to the predefined attachment points on the vehicle knuckle (4 - Figure 2) or through a stator plate (6 - Figure 2), where the stator plate is used for adapting to various vehicle attachment point layouts. These mounting points are on a diameter that assures unobstructed path for serviceable components, or in other words, is dimensioned in a way that the integrated serviceable component can be inserted and taken out of the stator.

When using the first embodiment of the locking tool (3), the rotor fixation holes (12) on the flat surfaces (1 1 ) each comprise a thread (14 - Figure 3) and are covered by sealing plugs (8) during the electrical machine operation, wherein also the stator fixation holes (22) on the flat surface (21 ) each comprise a thread (24 - Figure 3).

The first embodiment of the locking tool (3) comprises two parts, the first part being a screw (31 - Figure 6) with a thread (31 1 ) of a size and type matching the size and type of the thread (24) in the stator fixation holes (22), and the second part being an externally threaded tube (32 - Figure 6), wherein external thread (321 ) size and type of the tube matches the thread (14) size and type of the rotor fixation holes (12). The tube has an axially partial reduction of inner diameter on one end (322) for limiting axial movement of the screw, basically representing a seat for the screw head (312). On the other end of the tube there is a specific shape (324) used for mounting the tube onto the rotor fixation holes. The special shape refers to the matching geometry of a preferred tool used for mounting the locking tool.

When using the second embodiment of the locking tool (3), the rotor fixation holes (12) on the flat surfaces (1 1 ) each comprise an axially partial reduction of inner diameter (15 - Figure 4) for limiting axial movement of the screw (31 ), basically representing a seat for the screw head (312). This means that in this embodiment of the locking tool, the functional shape of an externally threaded tube (32) from the first locking tool embodiment was incorporated into the rotor (1 ) design. Sealing plugs (8) need to be put into the rotor fixation holes on the flat surfaces during the electrical machine operation in this embodiment, wherein each of the stator fixation holes (22) on the flat surface (21 ) comprises a thread (24 - Figure 3).

The second embodiment of the locking tool (3) comprises a screw (31 - Figure 4) with a diameter of its head (312) smaller than the diameter of a non-reduced inner diameter (17 - Figure 4) of the rotor fixation holes (12) on the flat surfaces (1 1 ), thus being the only maintenance part comprising this embodiment of locking tool.

When using the third embodiment of the locking tool (3), the diameter size of the rotor holes (12;18) on the flat surfaces (1 1 ) follows standardized interference fit recommendations, also known as shaft and holes fits, so as to enable tight fit with the locking tool. There is no need for sealing plugs (8) during the electrical machine operation, since this embodiment of locking tool does not need to be removed from the rotor (1 ), nor does this embodiment of locking tool require any tool for mounting. The diameter size of the stator fixation holes (22 - Figure 1 ; 28— Figure 5) on the flat surface (21 ) also follows standardized interference fit recommendations, so as to enable loose fit with the locking tool.

The third embodiment of the locking tool (3) comprises two parts, the first one being a tube (33

- Figure 7) with an outer diameter (331 ) of a size following standardized interference fit recommendations, enabling tight fit with the rotor fixation holes (12; 18) on the flat surfaces (1 1 ). The tube comprises also an inner diameter (332) of a size following standardized interference fit recommendations, enabling loose fit with an inner shaft (34 - Figure 7). The inner shaft is the second part of the locking tool according to the third embodiment and has a diameter (341 ) of a size following standardized interference fit recommendations, enabling loose fit with the stator fixation holes (22;28) on the flat surface (21 ).

In the main embodiment of this invention the mentioned electrical machine is an in-wheel motor (9 - Figure 2), comprising a bearing system inside the motor (10 - Figure 2), a brake disk (51 - Figure 2), a caliper (52 - Figure 2), and a seal or multiple seals (1 10 - Figure 2), or other serviceable components which are not removable while the stator is attached to the vehicle without the use of the locking tool (3). The bearing system, the brake disk and the caliper are all interchangeable with alternative design of the mentioned parts, either by using a custom adapter, by applying changes to the stator plate (6), or by changing the design of the vehicle attachment points.

A novel manufacturing method for the rotor-stator combination described above is performed using the following major steps; attaching the stator (2) to a special centering arrangement (610

- Figure 8) using the stator mounting points (23); attaching the rotor (1 ) to the centering arrangement using the rim mounting points (19 - Figure 9) inserting the locking tools (3) and removing the locked rotor-stator combination from the centering arrangement. The centering arrangement main function is to provide radial and axial constraints for the relative position of the rotor and stator before the locking tool is inserted, but it is desirable that the centering arrangement includes additional functions as described below.

In a preferred embodiment of the novel manufacturing method, the centering arrangement (610) is integrated with the production line pallet (620 - Figure 8) and allows relative rotation of the stator (2) and the rotor (1 ) by containing a bearing system (10). During the manufacturing the stator is attached to the centering arrangement through stator mounting points (23) with a quick mounting tool and the rotor is attached to the centering arrangement rotatable part with bolts through rim mounting points (19 - Figure 9). The end of line testing can then be performed on the assembly, including running the rotor and stator assembly, testing maximum torque and thermal properties. After the test is completed, the locking tools (3 - Figure 10) can be inserted and the locked assembly can be removed from the centering arrangement altogether and prepared for shipping. The centering arrangement (610 - Figure 1 1 ) returns with the pallet to the start of the assembly line.

Alternatively other embodiments of the manufacturing method are possible.

A method for performing maintenance work on serviceable parts of an in-wheel electric motor assembly of a vehicle comprises the following steps; unscrewing the main rim bolts (71 - Figure 1 ), removing the rim (7 - Figure 1 ), removing the sealing plugs (8) in the embodiments where they are required, mounting locking tools to rotor fixation holes (12) and stator fixation holes (22), thus locking relative position of stator and rotor, further removing stud bolts (101 - Figure 1 ) and the stator plate bolts (61 - Figure 2) if the motor is not mounted directly to the vehicle knuckle (4). The in-wheel motor rotor-stator combination (9) can then be moved aside without the need to disconnect it, and the brake system (5) can be serviced with the same access as in a conventional vehicle. The in-wheel motor rotor-stator combination can be easily removed by the mentioned procedure and the disconnection of the phase cables (25 - Figure 1), the cooling inlet (26 - Figure 1 ), and outlet (27 - Figure 1 ) can be achieved. Furthermore, the procedure can include in-wheel motor seal (1 10) service, where the brake system is not affected.

Using the locking tool has a big advantage, since the company producing the electric motors does not have to deal with logistics and storage of the brake system and bearing system with guarantees for their correct installation and tuning.

Claims

1. Rotor-stator combination (9) for an in-wheel electric motor assembly of a vehicle, the in- wheel electric motor assembly comprising: a bearing system (10) mounted to a knuckle of the vehicle for rotatably coupling a wheel rim (7) to the knuckle (4) of the vehicle, a brake (5), and the rotor-stator combination comprising a rotor (1 ) and a stator (2), wherein rotor and stator are arranged concentrically with respect to each other such that rotor and stator share a common motor axis (13), and wherein the rotor-stator combination has a first axial end facing the vehicle knuckle in a fully assembled state of the in-wheel electric motor assembly and a second axial end facing away from the vehicle knuckle in a fully assembled state of the in-wheel electric motor assembly, wherein the stator (2) comprises stator mounting points (23) for mounting the rotor-stator combination to the vehicle knuckle (4), wherein the rotor-stator combination has a hollow interior adapted to receive the bearing system (10) and the brake (5) in a fully assembled state of the in-wheel electric motor assembly, and wherein the rotor (1) comprises a plurality of rotor fixation holes (12) and the stator (2) comprises a plurality of stator fixation holes (22), wherein the rotor is lockable to the stator such that the concentric arrangement of rotor and stator is maintained without a bearing being arranged between rotor and stator, wherein locking the rotor to the stator is achievable by inserting a plurality of locking tools (3) into the plurality of rotor fixation holes and into the plurality of stator fixation holes, wherein each of the plurality of locking elements is inserted into one of the plurality of rotor fixation holes and into a corresponding one of the plurality of stator fixation holes, characterized in that an opening of the rotor-stator combination at the first axial end of the rotor-stator combination facing the knuckle and leading into the hollow interior of the rotor-stator combination is designed such that the rotor-stator combination can be mounted to and dismounted from the vehicle knuckle as a unit without the need to remove the bearing system and/or the brake from the vehicle knuckle, wherein the stator mounting points are arranged at such a distance from the motor axis that the stator mounting points do not interfere with the bearing system and brake when the rotor-stator combination is mounted to or dismounted from the vehicle knuckle.

2. Rotor-stator combination according to claim 1 , characterized in that each of the rotor fixation holes (12) is arranged at the same radial distance from the motor axis (13) as the corresponding stator fixation hole (22) such that the axes of said rotor fixation hole and said corresponding stator fixation hole coincide.

3. Rotor-stator combination according to claim 1 or 2, characterized in that an opening of each of the rotor fixation holes is surrounded by a first flat surface (11) of the rotor that is perpendicular to the axis of the respective rotor fixation hole (12), wherein an opening of each of the stator fixation holes (22) is surrounded by a second flat surface (21 ) of the stator that is perpendicular to the axis of the respective stator fixation hole (22).

4. Rotor-stator combination according to one of claims 1 to 3, characterized in that the rotor fixation holes (12) are located on an axial side surface (16) of the rotor (1) facing the rim (7), wherein the stator holes (22) are located close to the axial side surface of the rotor facing the rim without obstructing the bearing system and the brake.

5. Rotor-stator combination according to one of claims 1 to 4, characterized in that each of the rotor fixation holes (12) comprises a threaded portion (14) into which the corresponding locking tool (3) can be screwed, wherein each of the stator fixation holes (22) also comprises a threaded portion (24) into which the corresponding locking tool (3) can be screwed.

6. Rotor-stator combination according to one of claims 1 to 4, characterized in that each of the stator fixation holes (22) comprises a threaded portion (24) into which the corresponding locking tool (3) can be screwed.

7. Rotor-stator combination according to claim 6, characterized in that each of the rotor fixation holes (12) comprises an axial portion of reduced inner diameter (15).

8. Rotor-stator combination according to any one of claims 1 to 7, characterized in that the rotor-stator combination further comprises a plurality of sealing plugs (8) insertable into the plurality of rotor fixation holes (12).

9. System for assembling and/or servicing an in-wheel electric motor, with a rotor-stator combination according to one of claims 1 to 8 and with a plurality of locking tools (3), wherein the rotor (1) is locked to the stator (2) for assembling and/or servicing purposes in that each of the plurality of locking elements is inserted into one of the plurality of rotor fixation holes (12) and into a corresponding one of the plurality of stator fixation holes (22).

10. System according to claim 9 with a rotor-stator combination according to claim 5, characterized in that each locking tool (3) comprises a screw (31 ) with a thread (31 1 ) of size and type matching the size and type of the threaded portion (24) of the stator fixation holes (22), and an externally threaded tube (32), wherein the size and type of an external thread (321 ) of the tube matches the size and type of the threaded portion of the rotor fixation holes (12), wherein the tube, on one end thereof, comprises an axial portion of reduced inner diameter (322) for limiting axial movement of the screw, and wherein the tube, on another end thereof, comprises a specific shape (324) for mounting the tube onto the rotor fixation hole.

1 1 . System according to claim 9 with a rotor-stator combination according to claim 6 or 7, characterized in that each locking tool (3) comprises a screw (31 ) with a thread (31 1 ) of size and type matching the size and type of the threaded portion (24) of the stator fixation holes (22), wherein a head (312) of the screw is smaller in diameter than a diameter of an axial portion of the rotor fixation holes (12) with non-reduced inner diameter (17).

12. System according to claim 9, characterized in that the diameter size of the rotor holes (12; 18) follows standardized interference fit recommendations so as to enable tight fit with the locking tool (3), wherein the diameter size of the stator holes (22; 28) follows standardized interference fit recommendations so as to enable loose fit with the locking tool.

13. System according to claim 12, characterized in that the locking tool (3) comprises a tube (33) and an inner shaft (34), wherein the tube (33) has an outer diameter (331 ) of a size following standardized interference fit recommendations enabling tight fit with the rotor fixation holes (12; 18), wherein said tube comprises an inner diameter (332) of a size following standardized interference fit recommendations enabling loose fit with the inner shaft (34), and wherein said inner shaft has a diameter (341 ) of a size following standardized interference fit recommendations enabling loose fit with the stator holes (22; 28).

14. In-wheel electric motor assembly of a vehicle, comprising a bearing system (10) mounted to a knuckle (4) of the vehicle for rotatably coupling a wheel rim (7) to the knuckle (4) of the vehicle, a brake (5), and a rotor-stator combination according to one of claims 1 to 8.

15. In-wheel electric motor assembly according to claim 14, characterized in that the brake (5) comprises a brake disk (51 ) and a caliper (52), wherein the in-wheel electric motor assembly further comprises a seal or multiple seals (1 10) or other serviceable components, and wherein the bearing system, the brake, the seal of multiple seals and the other serviceable components are not removable while the stator (2) is attached via the stator mounting points (23) to the vehicle.

16. In-wheel electric motor assembly according to claim 15, characterized in that the bearing system (10) is interchangeable with another bearing system design using a custom adapter, a change of the stator plate (6), or a different design of respective vehicle attachment points, wherein the brake disc (51 ) and the caliper (52) are interchangeable with another brake disc and caliper design using a custom adapter, a change of the stator plate, or a different design of respective vehicle attachment points.

17. A method of manufacturing a rotor-stator combination, particularly according to one of claims 1 to 8, the method comprising the steps of: mounting a rotor (1 ) and a stator (2) on a centering arrangement (610), locking relative position of rotor (1 ) and stator (2) with at least one locking tool (3); and detaching the locked rotor-stator combination from the centering arrangement.

18. The method according to claim 17, wherein the centering arrangement (610) provides radial and axial constraints for the relative position of rotor (1 ) and stator (2) and allows relative rotation of rotor and stator.

19. The method according to claim 17 or 18, wherein the locking step comprises mounting a plurality locking tools (3) to a plurality of rotor fixation holes and a plurality of stator fixation holes that are evenly spaced around the circumference of the rotor-stator combination.

20. The method according to one of claims 17 to 19, wherein an intermediate step of rotor (1 ) and stator (2) assembly dynamic testing is performed before the locking step.

21 . The method according to one of claims 17 to 20, wherein the centering arrangement (610) is reused for the manufacturing of another rotor-stator combination after the locked rotor-stator combination has been detached from the centering arrangement.

22. The method according to one of claims 17 to 21 , wherein the method further comprises shipping the locked rotor-stator combination without installing a bearing system (10) or a brake system (5) to the rotor-stator combination.

23. A method of performing maintenance work on serviceable parts of an in-wheel electric motor assembly of a vehicle, particularly according to one of claims 14 to 16, the method comprising the steps of: removing a vehicle wheel of the in-wheel electric motor assembly; locking relative position of a rotor (1) and a stator (2) of a rotor-stator combination of the in-wheel electric motor assembly with at least one locking tool (3); and unmounting the rotor-stator combination from mounting points of the vehicle and moving the rotor-stator combination aside without disconnecting it from the vehicle, thereby enabling maintenance of the serviceable components.

24. The method according to claim 23, wherein removing the vehicle wheel comprises unscrewing rim bolts (71) and removing a rim (7) of the vehicle wheel, wherein the locking step comprises mounting a plurality locking tools (3) to a plurality of rotor fixation holes and a plurality of stator fixation holes that are evenly spaced around the circumference of the rotor- stator combination.

25. The method according to claim 24, wherein sealing plugs (8) are removed from the rotor fixation holes (12) before mounting the plurality of locking tools to the plurality of rotor fixation holes and the plurality of stator fixation holes.

26. The method according to claim 24 or 25, wherein the unmounting step comprises removing stator plate bolts (61 ) and stud bolts (101 ).